Richard Quinn
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| posted on 18/2/08 at 11:56 AM |
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Rear harness mounts and SVA - Discussion point
Firstly, I know that “the rules is the rules” and all that but, having dry fitted my seat in the car at the weekend, the more I think about the rear
seat belt/harness mounting measurement requirements, the more issues I have with them.
I’m guessing that the requirements have their origins in conventional car seats and seat belts rather than “race type” fibreglass seats and 4+ point
harnesses and, IMHO, applying this to the fibreglass seat and 4+ point harness arrangement could lead to more safety issues than it addresses.
Now I may be talking out of my ar*e here and I am fully willing to be corrected but… if you raise the front of your seat so as to adopt a more laid
back position, this has the effect of lowering your shoulders with respect to the top rear harness mounts. However, this would also have the effect of
raising the point from which the total 503mm is measured meaning that the mounting mounts would have to be raised. So, as the shoulders go down, the
harness mounting points have to be raised??? I don’t know how many of you have ever been upside down in a car fitted with harnesses but I can assure
you that you really wouldn’t want a gap between your shoulders and the top harness mounts!
I appreciate that a more reclined position can lead to an increased risk of submarining but this is usually at least partially addressed by the use of
5 or 6 point harnesses.
Am I missing something here or am I understanding the situation correctly? - Please discuss...
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Mr Whippy
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| posted on 18/2/08 at 12:07 PM |
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I may not be sufficiently caffeinated right now but I was under the impression that the harness mounting hight was taken from the back of the seat
base and not the front.
[Edited on 18/2/08 by Mr Whippy]
Fame is when your old car is plastered all over the internet
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02GF74
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| posted on 18/2/08 at 12:12 PM |
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quote:
Originally posted by Richard Quinn
if you raise the front of your seat so as to adopt a more laid back position, this has the effect of lowering your shoulders with respect to the top
rear harness mounts. However, this would also have the effect of raising the point from which the total 503mm is measured meaning that the mounting
mounts would have to be raised. So, as the shoulders go down, the harness mounting points have to be raised???
What exactly is the question?
When you talk about raising the front, depending on how this is achieved may or may not affect the reference point from which the mounting point
height is measured, see below.
 
annex4
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Richard Quinn
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| posted on 18/2/08 at 12:16 PM |
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I thought it was 450mm from a block/box 136mm long and 53mm high. This means that the measurement is taken from a point 136mm from the back of the
seat. So, as you tilt the seat back, surely this point would raise up??
Sorry, posted too slowly!
If you pivot the seat backwards on the rear of the base then surely the reference point also travels in an arc up and back??
It's not so much of a question, more of an observation that I am requesting confirmation or otherwise of.
[Edited on 18/2/08 by Richard Quinn]
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Howlor
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| posted on 18/2/08 at 12:26 PM |
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I am sure I remember a topic on here some time ago were if the seat is structural then you are ok with a lower mount and the harness can pass over the
harness hole.
I think it referred to Cobra seats were someone got a letter from them to state they were structural and could therefore take the force of the harness
bearing down on the harness hole.
On mine I used some 12mm steel bush crush tubes to raise them up and it was absolutely fine.
Just something else to add to the equation!
Steve
[Edited on 18/2/08 by Howlor]
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Mr Whippy
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| posted on 18/2/08 at 12:27 PM |
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Remember this is just for the SVA anyway, so if you’re not happy with the setup then there's nothing stopping you changing it later to suit
yourself. The sizes 136mm long and 53mm high are stupidly precise for something as varied as people shapes anyway (usually the sign of something
trivial done up to look important).
Fame is when your old car is plastered all over the internet
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smart51
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| posted on 18/2/08 at 01:05 PM |
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the reference point is roughly where your hip joint is.
[Edited on 18-2-2008 by smart51]
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russbost
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| posted on 18/2/08 at 01:28 PM |
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You are quite right in what you say. The problem is that the SVA is not designed specifically to deal with kit vehicles, but with a whole multitude of
designs AND kits. What is right for a Seven or a car like mine isn't going to be right for a tourer style vehicle.
It is unfortunate that the rules leave no margin for interpretation or for different application to specific types of vehicle - if they did then you
would get more problems with cars failing at one centre that would pass at another & there's a fair bit of that already, all testers seem to
have their own area they look at more closely than others.
Usual story of government applying rules for "one size fits all"
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Richard Quinn
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| posted on 18/2/08 at 02:12 PM |
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Thanks Russ. I just can't understand why seat belt criteria are applied to harnesses. In most (not all) cases, harnesses are there to keep you
both down and back and are generally designed to be fitted something similar to below...
[img][/img]
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Richard Quinn
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| posted on 18/2/08 at 02:17 PM |
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... and (extreme example I know before I get shot down!!) what if you wanted to fit one of these to one of Russ' cars (it is quite in keeping!).
Where would your rear harness mounts have to be relative to your shoulders?? (and no comments about me being worried about safety when the car is made
out of plastic plumbing! It's not mine and I believe it is a bit of a mock up!)
[img][/img]
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Howlor
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| posted on 18/2/08 at 02:51 PM |
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quote:
Originally posted by Richard Quinn
Thanks Russ. I just can't understand why seat belt criteria are applied to harnesses. In most (not all) cases, harnesses are there to keep you
both down and back and are generally designed to be fitted something similar to below...
Image deleted by owner
Yes I agree but most FIA seats are designed to take a vertical compression load in an accident so if the belt rests on the seat then onto your
shoulders if the seat gives way in an accident you move forward a considerable amount more.
Isnt the 20 degrees inclination a maximum in the new blue book? They prefer I think a horizontal pull.
Steve
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Richard Quinn
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| posted on 18/2/08 at 03:11 PM |
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I'm not talking about whether the harness touches the seat or not, just the relationship between the mounting position and the shoulders. In
this hypothetical situation the harness can still rise 20deg straight to the shoulders without fouling the harness holes in the seat.
Incidentally, I would guess that there are more injuries caused by incorrectly located mounting mounts for the 5th on 6th points or harnesses. Many
people seem to fix them too far back under the seat and you would be amazed how a crotch strap will cut through the base of a fibreglass seat like a
cheesewire which can suddenly lead to quite a bit of slack in the harness just when you really don't need it!
[Edited on 18/2/08 by Richard Quinn]
[Edited on 18/2/08 by Richard Quinn]
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NS Dev
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| posted on 18/2/08 at 07:42 PM |
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My take on it would be that your point is quite right Rich, but they have to emasure it somehow and the test is "tailored" to a more
upright seating position.
I can certainly say that the rig they use to check the seat would be tipped backwards by the inclination, though the rig is like a rectangular
baseplate with a column in the middle with a string on it. He pulls the string back level checked with a spirit level (car on level ground) then makes
sure the harness mounts are at or below the string level.
With this rig, the top of the rig would lower very slightly as the chair was tipped, but only very slightly.
If in doubt, there's a simple solution......read your seating section in the sva manual carefully, the section about lift out seat squabs!!
I used two pieces of hardboard with old car seat leather stapled over them!!
The "seat" base is then about 5mm thick, job done.
I'm pretty sure I could have passed with no seat in there at all.
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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Richard Quinn
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| posted on 18/2/08 at 07:59 PM |
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As a slight aside - If you were to go for an eye bolt type mounting, is the mounting point considered to be the centre of the eye?
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NS Dev
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| posted on 18/2/08 at 10:54 PM |
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I believe so, it would be the point it pulled from when under load.
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
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NS Dev
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| posted on 18/2/08 at 10:55 PM |
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PS if not its easy to use bolt on mounts and spacer them up
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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